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Question Number 144199 by qaz last updated on 23/Jun/21
Prove that                1+(1^2 /(6+(3^2 /(6+(5^2 /(6+(7^2 /(6+(9^2 /(6+...))))))))))=(2/(1+((1×2)/(1+((2×3)/(1+((3×4)/(1+((4×5)/(1+((5×6)/(1+...))))))))))))
$$\mathrm{Prove}\:\mathrm{that} \\ $$$$\:\:\:\:\:\:\:\:\:\:\:\:\:\:\mathrm{1}+\frac{\mathrm{1}^{\mathrm{2}} }{\mathrm{6}+\frac{\mathrm{3}^{\mathrm{2}} }{\mathrm{6}+\frac{\mathrm{5}^{\mathrm{2}} }{\mathrm{6}+\frac{\mathrm{7}^{\mathrm{2}} }{\mathrm{6}+\frac{\mathrm{9}^{\mathrm{2}} }{\mathrm{6}+…}}}}}=\frac{\mathrm{2}}{\mathrm{1}+\frac{\mathrm{1}×\mathrm{2}}{\mathrm{1}+\frac{\mathrm{2}×\mathrm{3}}{\mathrm{1}+\frac{\mathrm{3}×\mathrm{4}}{\mathrm{1}+\frac{\mathrm{4}×\mathrm{5}}{\mathrm{1}+\frac{\mathrm{5}×\mathrm{6}}{\mathrm{1}+…}}}}}} \\ $$
Answered by Dwaipayan Shikari last updated on 23/Jun/21
(π/4)=1−(1/3)+(1/5)−(1/7)+..=1+(−(1/3))+(−(1/3))(−(3/5))+...  =(1/(1+((1/3)/(1−(1/3)+((3/5)/(1−(3/5)+((5/7)/(1−(5/7)+((7/9)/(1−(7/9)..))))))))))=(1/(1+(1^2 /(2+(3^2 /(2+(5^2 /(2+(7^2 /(2+..))))))))))  tan^(−1) x=x−(x^3 /3)+(x^5 /5)−(x^7 /7)+...  =(x/(1+((x^2 /3)/(1−x^2 /3+((3x^2 /5)/(1−3x^2 /5+..))))))=(x/(1+(x^2 /(3−x^2 +((3^2 x^2 )/(5−3x^2 +((5^2 x^2 )/(7−5x^2 +..)))))))).  ...
$$\frac{\pi}{\mathrm{4}}=\mathrm{1}−\frac{\mathrm{1}}{\mathrm{3}}+\frac{\mathrm{1}}{\mathrm{5}}−\frac{\mathrm{1}}{\mathrm{7}}+..=\mathrm{1}+\left(−\frac{\mathrm{1}}{\mathrm{3}}\right)+\left(−\frac{\mathrm{1}}{\mathrm{3}}\right)\left(−\frac{\mathrm{3}}{\mathrm{5}}\right)+… \\ $$$$=\frac{\mathrm{1}}{\mathrm{1}+\frac{\mathrm{1}/\mathrm{3}}{\mathrm{1}−\frac{\mathrm{1}}{\mathrm{3}}+\frac{\mathrm{3}/\mathrm{5}}{\mathrm{1}−\frac{\mathrm{3}}{\mathrm{5}}+\frac{\mathrm{5}/\mathrm{7}}{\mathrm{1}−\frac{\mathrm{5}}{\mathrm{7}}+\frac{\mathrm{7}/\mathrm{9}}{\mathrm{1}−\frac{\mathrm{7}}{\mathrm{9}}..}}}}}=\frac{\mathrm{1}}{\mathrm{1}+\frac{\mathrm{1}^{\mathrm{2}} }{\mathrm{2}+\frac{\mathrm{3}^{\mathrm{2}} }{\mathrm{2}+\frac{\mathrm{5}^{\mathrm{2}} }{\mathrm{2}+\frac{\mathrm{7}^{\mathrm{2}} }{\mathrm{2}+..}}}}} \\ $$$${tan}^{−\mathrm{1}} {x}={x}−\frac{{x}^{\mathrm{3}} }{\mathrm{3}}+\frac{{x}^{\mathrm{5}} }{\mathrm{5}}−\frac{{x}^{\mathrm{7}} }{\mathrm{7}}+… \\ $$$$=\frac{{x}}{\mathrm{1}+\frac{{x}^{\mathrm{2}} /\mathrm{3}}{\mathrm{1}−{x}^{\mathrm{2}} /\mathrm{3}+\frac{\mathrm{3}{x}^{\mathrm{2}} /\mathrm{5}}{\mathrm{1}−\mathrm{3}{x}^{\mathrm{2}} /\mathrm{5}+..}}}=\frac{{x}}{\mathrm{1}+\frac{{x}^{\mathrm{2}} }{\mathrm{3}−{x}^{\mathrm{2}} +\frac{\mathrm{3}^{\mathrm{2}} {x}^{\mathrm{2}} }{\mathrm{5}−\mathrm{3}{x}^{\mathrm{2}} +\frac{\mathrm{5}^{\mathrm{2}} {x}^{\mathrm{2}} }{\mathrm{7}−\mathrm{5}{x}^{\mathrm{2}} +..}}}}. \\ $$$$… \\ $$

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